Windows 7, Vista Switch IDE to AHCI

If you have installed your Windows 7 with the AHCI turned off in BIOS, but out of a sudden AHCI is required (for example to run OSX) it is still possible to change the setting without leaving Windows 7 ubootable.

According to

It is required to change two registry entries BEFORE you make any changes in BIOS

  1. Click Start and in the “search” field enter regedit, then press Enter
  2. If User Account Control dialog shows up, allow Registry Editor by clicking Continue.
  3. Find the following keys in registry:
  4. Find the “Start” variable in the right pane, right click it and choose Modify.
  5. Change the value from 3 to 0. Repeat the same steps for both services mentioned in step 3
  6. Close Registry Editor.
  7. Reboot your computer and press DEL or F12 to enter BIOS
  8. Change the controller mode from IDE to AHCI
  9. Choose “Save and exit setup“, confirm with a ‘Y’ if necessary.
  10. Done, your Windows 7 should boot without problems.


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